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We present approaches using stochastic processes for the calculation of line broadening in plasmas. The derivation of model microfield methods (MMM) based on analytic formulations is recalled, as well as an approach using a simulation of the stochastic process. We discuss the possibility of an improvement of the stochastic process by comparing our first results to ab initio particle simulations coupled to a numerical integration of the emitters Schrödinger equation.

• The motional Stark broadening of spectral lines is investigated in the case of plasmas subject to a large external magnetic field. • A line shape model that accounts for atomic velocity changes due to collisions is proposed. • It is shown that such collisions significantly affect the line broadening. The shape of spectral lines in strongly magnetized plasmas is investigated theoretically in the framework of astrophysical research. Under certain conditions, the broadening of lines observed on white dwarf spectra is dominated by the so-called motional Stark effect, which occurs due to the Lorentz electric field v → × B →. If the plasma density is high enough, collisions between the emitter and perturbers change the atomic velocity v → and the resulting motional Stark broadening is modified. We illustrate this modification through dedicated line shape calculations based on a stochastic model for the atomic velocity. A universal line shape formula, which is applicable to any isolated atomic line, is proposed for implementation in line shape codes. [ABSTRACT FROM AUTHOR]

A computer simulation technique is applied to the modelling of Balmer line shapes in dense divertor conditions. The spectral profile of lines with a high principal quantum number n is sensitive to Stark broadening and can be used as a density diagnostic. In contrast, an analysis of the shape of low or moderate n lines such as Dα (n = 3), Dβ (n = 4), and Dγ (n = 5) is more intricate because the Stark effect is weaker and can compete with thermal Doppler broadening. We examine this issue and address the relative contribution of the Stark and Doppler effects on the first Balmer lines. Analyses of experimental spectra are performed. [ABSTRACT FROM AUTHOR]

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman a line in an ideal one-component plasma. A focus is put on the central Zeeman component. It is shown that the atomic dipole autocorrelation function decreases more slowly if the cyclotron motion is retained. In the frequency domain, this denotes a reduction of the line broadening. A discussion based on numerical simulations and analytical estimates is done. [ABSTRACT FROM AUTHOR]

Spectral profiles of the D γ line have been calculated in magnetic fusion plasma conditions for diagnostic purposes. This paper reports on the elaboration of a table devoted to spectroscopic applications in tokamak divertors. An overview of the method, together with the physics underlying the broadening of spectral lines, is given. A special emphasis is put on the role of the simultaneous action of the Stark and Zeeman effects. [ABSTRACT FROM AUTHOR]

Stochastic processes may be used as an efficient model for the line shapes affected by Stark effect in edge plasma conditions. We check the accuracy of this approach on the Lyman γ line of hydrogen perturbed by ions only. We also use a stochastic process to investigate the effect of plasma oscillations on a line shape. Our model assumes that Langmuir waves are a sequence of oscillating electric fields changing their amplitude and phase according to an exponential waiting time distribution. The possible effects of Langmuir waves on the Lyman α Stark profile are discussed in edge plasma conditions. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) formalism is revisited in the framework of plasma spectroscopy. We address the issue of Stark line shape modeling by using kinetic transport equations. In the most simplified treatment of these equations, triple correlations between an emitter and the perturbing charged particles are neglected and a collisional description of Stark effect is obtained. Here we relax this assumption and retain triple correlations using a generalization of the Kirkwood truncature hypothesis to quantum operator. An application to hydrogen lines is done in the context of plasma diagnostic. It is shown that the neglect of triple correlations can lead to a significant overestimate of the line width. [ABSTRACT FROM PUBLISHER]

Stark broadening of hydrogen lines is investigated in low-density magnetized plasmas, at typical conditions of magnetic fusion experiments. The role of time ordering is assessed numerically, by using a simulation code accounting for the evolution of the microscopic electric field generated by the charged particles moving at the vicinity of the atom. The Zeeman effect due to the magnetic field is also retained. Lyman lines with a low principal quantum number n are first investigated, for an application to opacity calculations; next Balmer lines with successively low and high principal quantum numbers are considered for diagnostic purposes. It is shown that neglecting time ordering results in a dramatic underestimation of the Stark effect on the low-n lines. Another conclusion is that time ordering becomes negligible only when ion dynamics effects vanish, as shown in the case of high-n lines. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the role of turbulent fluctuations on line shape formation in optically thin plasmas. A general expression, valid if the turbulent scales are much larger than the atomic scales, is obtained for the profile measured using a passive spectroscopy set up. Well-known limiting cases for Doppler and Stark broadening are identified. Then, the role of temperature fluctuations on Doppler line shapes, and the effect of density fluctuations on Stark broadened lines in the quasi-static regime are investigated. [Copyright &y& Elsevier]

Abstract: Ion dynamics is revisited in the presence of a magnetic field. This problem is of interest for the characterization of the ITER divertor plasmas, where Zeeman–Stark line shapes are both a diagnostic tool and an ingredient in the transport codes used for radiative transfer simulations. Comparisons between ab initio simulations of Zeeman–Stark profiles and calculations performed using the computationally efficient frequency fluctuation model are presented for the Lyman α and Balmer α lines. [Copyright &y& Elsevier]

Abstract: Hydrogen line radiation can be trapped in some spatial regions within magnetic fusion experiments at high density, typically when N H(∼N e)∼1015 cm−3. The corresponding photoexcitation yields a significant additional source of ionization that must be properly characterized by numerical simulations. Kinetic Monte-Carlo codes provide a capability to study this subject; however, these codes require accurate physical models for the reaction rates, including spectral line shapes. In this paper we deal with the Zeeman–Stark model used for the Lyα transition in the EIRENE code [D. Reiter, M. Baelmans, P. Börner, Fusion Sci. Technol. 47 (2005) 172; www.eirene.de] and we address the influence of ion dynamics, which can affect these line profiles. The impact theory for ions, that we first consider, is shown to be suited for description of the lateral components of the Lorentz triplet. By contrast, comparisons to numerical simulations show that this theory is not well suited for description of the central component, which is significantly affected by incomplete and non-binary collisions. A refinement of the model in the framework of the unified theory is proposed and discussed. [Copyright &y& Elsevier]

The divergence that occurs at large impact parameters in Stark collision operators is examined for low-density hydrogen plasmas. In a previous work [J. Rosato, H. Capes, and R. Stamm, Phys. Rev. E 86, 046407 (2012)], we showed that the correlations between a radiating atom and the charged particles surrounding it affect the mean evolution of the atom, resulting in a mitigation of the Stark broadening near the line center. In this work, we examine the physical mechanism underlying this mitigation with an approach inspired from the standard semiclassical impact model. Our approach accounts for the atom-perturber correlations in a simple fashion, through a cutoff at large impact parameters, and embraces the impact model in the weakly coupled plasma limit. Comparisons with numerical simulations are performed and indicate a good agreement. [ABSTRACT FROM AUTHOR]

• The trapping of atomic line radiation in high-density divertor plasmas is examined. • The mechanisms underlying line broadening, such as Doppler and Stark effects, are shown to strongly affect the photoexcitation rate. • Monte Carlo simulations of the radiation transport in slab geometry are performed as an illustration. In divertor plasmas at high density regimes, typically with N e larger than 1014 cm − 3 , the photons emitted in the resonance line of the hydrogen isotopes have a mean free path that can be as short as one millimeter. They provide an additional source of excited atoms, which can be ionized more easily; a consequence of this is that the whole ionization-recombination balance of the divertor plasma can be altered. In this work, we investigate the influence of the spectral line profile on the photoexcitation rate. A kinetic Monte Carlo solver is applied to the transport of photons in slab geometry. The relative contribution of the Doppler and Zeeman effects on the line profile is examined. In the framework of ITER nuclear phase preparation, we also examine the influence of deuterium and tritium line shape overlapping and we address the transport of the helium resonance line radiation. [ABSTRACT FROM AUTHOR]

We examine atomic line shapes in a magnetized hydrogen plasma. The Lorentz electric field v × B present in the emitters' frame of reference yields a perturbation of the atomic energy levels, which is commonly referred to as a ‘motional’ Stark effect. This effect results in a broadening of the lines owing to the statistical repartition of the atoms' velocities. We address this line broadening mechanism with numerical simulations. It is shown that Balmer line shapes can be affected at plasma conditions relevant to magnetic fusion experiments. An application to the diagnostic of an atomic temperature is suggested and discussed within a line width analysis. The possibility for a modification of the Inglis–Teller limit, which provides an estimate of the principal quantum number of the last resolved line in a series, is also discussed. [ABSTRACT FROM AUTHOR]

Stochastic processes provide flexible and fast calculations for modeling dynamical interactions between an atom and charged particles. We use a stochastic renewal process for the plasma microfield being the cause of Stark broadening. The accuracy and improvement possibilities of Lyman profiles calculations with a renewal process are analyzed by comparing to ab initio simulations for ion broadening only. Stochastic processes may also be applied to out of equilibrium plasmas. We present our first results for the effect of Langmuir waves on a line broadened by electrons only, and for the changes of atomic populations submitted to strong temperature fluctuations. [ABSTRACT FROM AUTHOR]

Abstract: An overview of several spectral line shapes studies of common interest in astrophysical and laboratory plasmas is presented. For lines dominated by Stark broadening, approaches taking into account the dynamics of numerous perturbers are sometimes required. We briefly recall ab initio simulation techniques and model microfield methods used for such conditions. Together with the impact approximation, such models may also be used for studying the effects on a line profile of a magnetic field of the order of the tesla, allowing the diagnostic of stellar objects or magnetic fusion devices. The problem of the apparent spectral line emitted in a plasma affected by strong fluctuations of the plasma parameters is discussed for the case of optically thin plasmas. [Copyright &y& Elsevier]

Abstract: The n =5–6 (λ =4658Å) and n =6–7 (λ =7726Å) spectral lines emitted by Li-like carbon ions C+3 from magnetic fusion devices based on carbon material are considered for plasma diagnostic purposes. The broadening mechanisms of these lines are examined for plasma conditions relevant to Tokamak divertors (electron densities and temperatures in the ranges 1019–1021 m−3 and 1–10eV). Under these conditions, the broadening mechanisms affecting the above lines are examined with and without the retaining of the magnetic field. The uncertainties on the deduced plasma parameters are also qualitatively estimated when only Stark and Doppler effects are retained while Zeeman and fine structure effects are ignored. The results presented are based on theoretical calculations carried out with the PPP line shape code and an atomic data basis built using Cowan’s code and the most accurate available atomic data for carbon. [Copyright &y& Elsevier]